Change prepack npm script to prepare (take 2) (#1755)

* update truffle to include bugfix

* change prepack script to prepare

* add npx in compile script

* fix for older node

* rename script file to prepare

(cherry picked from commit 036dd9bd6e)

scripts/compile.sh

@@ -4,7 +4,4 @@ if [ "$SOLC_NIGHTLY" = true ]; then
   docker pull ethereum/solc:nightly
 fi
 
-# Necessary to avoid an error in Truffle
-rm -rf build/contracts
-
-truffle compile
+npx truffle compile